Making my own reflow hot plate - Part 1 - Prototype
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- เผยแพร่เมื่อ 13 เม.ย. 2022
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In this video, I show you the prototype of my reflow hot plate. The hot plate is just a simple "desoldering heating plate" that you can buy from popular webshops. However, the coding part, especially the graphical user interface (GUI) is much more sophisticated. I created a fancy GUI that allows the user to enter any arbitrary reflow curve and then run the program and follow the development of the temperature in real-time. The circuit also has a MAX6675 thermocouple module for measuring the temperature and a simple BD139-based transistor circuit that switches on two tiny fans at the end of the program to speed up the cooling/solidification process.
In the upcoming videos, I will put these things on a proper PCB and further improve the coding part and will try different heaters.
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I also tried to build one, but the temperature sensor is just to slow for a good PID control (like the blue bumpy temperature graph). Then I used a Mlx90614 sensor to read the temperature and now it's much more precise.
Hi! I don't have issues with the speed of the temperature reading. I can go really fast. Now I read it every 250 ms, and the TRIAC program checks the temperature every 1 s. I think the issue is, especially at low temperatures, that the PTC draws too high current which results in a large overshoot. I will fix this with some software tricks and try if it works.
How slow is too slow?
If you preemptively turned the heater off at a lower temp than required, you may be able to minimise overshoot.
Hi! Thanks, that is a great idea! What I will do is I will come up with some kind of multiplier that will change as a function of the temperature. The higher the temperature, the longer the TRIAC will be kept switched on. Actually, I mentioned this stuff a few days ago on my IG. The large overshoots at low temperatures are due to the (natural) behaviour of the PTC heater. While it is "cold", its resistance is low, so when I turn it on, a large current can flow through it. When it is properly heated up, its resistance is higher, so when it is turned on, the current is already limited, thus the overshoot is much lower. I will implement something and publish it in an upcoming video.
That's what the D term of a PID controller does.
Think with a ptc heated bed you lose some of the power since it's a linear increase of resistance, it doesn't just stop after a temperature limit, it gradually gets lower and lower power. The alternative would be using a simple resistive heated bed (you could even diy one for your exact power requirements using aluminium based PCBs), but that has safety issues since if your control circuit fails it can get red hot and set stuff on fire. To mitigate that you could use a failsafe like a bimetalic cutoff switch at a higher temperature than you'll ever need in series with the mains.
I like the UI, looks really nice.
For the curve using a PID controller with a platinum temperature sensor should be able to achieve a really smooth curve.
One of the heaters I ordered is a resistive heater. A Kanthal wire is wrapped around a mica plate which is then sandwiched between 2 other mica plates, and this whole stuff is encapsulated in thin stainless steel sheets. I also ordered some of those ceramic heaters which can be found on those BGA rework stations. Just to play around with stuff. The platinum thermometer would be nice, but they are slow and expensive. At least those which are easily available. I can use the thermocouple easily and they are cheap. I could even spot-weld it on certain surfaces for good thermal contact. Regarding the UI, thank you so much! I worked a lot on it to figure out all the stuff and create a decent interface.
@@CuriousScientist the 2x2.3mm platinum RTD sensors are quite affordable (under 5 GBP) and have very quick response.
Hi! Yes, wrong phrasing from my side. The sensor itself is of course quick, but the circuit (max31865) is slow and also expensive.
@@CuriousScientist Most of the delay is probably down to the mass of the hotplate itself and the heat conduction delay. To stabilise the control loop then needs a long integration time. For the precision hotplate controls that I build I use cascaded controllers with a separate sensor on the heater element itself. An RTD on the hotplate and a differential thermocouple between that and the element.
You can make a proportinal heating by switch the triac every second with a chosen duty cycle.
I know. I do almost the same but the duty cycle is 100%. 😅
Nice project! Every person making soldering devices must face that temperature overshooting, is something inevitable, I saw a few videos with different solutions, I will be waiting your next installment to see how you overcome that.
Oh, and I will remember the brown from now on 💩😅
Thank you! Yes, I agree, the overshooting is inevitable, but at least it can be mitigated to a certain degree (pun intended). My PCB is on its way, so as soon as I get it, a new video will come out and I will try to show my way of dealing with the overshoot. Some viewers already gave me really good ideas.
Because it's AC, both mains wires, brown and blue, will manage to fry your pants off if you manage to make a connection. The AC signal is symmetrical on both, although one from the perspective of the other will be 180 degree out of phase to the other way around. The biggest difference is if one has more resistance to the ground wire vs the other. So I never understood the concept of 'neutral' wire. They both hot!!
Yes, you're correct. This was a more "funny" explanation for those who are like me and always forget the naming of the wires. In any case, it is not advised to touch any of those wires anyway.
@ivolol This depends on the supply. In the UK for example the neutral is grounded at the substation transformer so that the neutral in the home is never more that a few volts from ground (or earth as we call it). So the line (brown) wire is a sine wave of 230V rms (usually rather more) centred around ground. This is usually the case for single phase supplies throughout Europe.
I have always remembered my aunt telling me that "George Brown is a live wire" back when the colour change first came in (George Brown was a well known politician back then).
I just independently ordered the same hot plate for the same type of project. And now I find this video. AI?
I keep my eyes on you 👀
code please!
It's available on my Patreon page.
Bah ha ha, ".... remember the brown, if you touch the brown you will shit your pants and your pants will be brown"
That is brilliant!
Haha, I am glad that you noticed this part. And I hope, from now you will remember which wire is the brown. 😄
Where are the software specs and the sketch ?
On my Patreon site.